Evidence suggests the various signs and consequences of skin aging may be connected to cumulative oxidative damage incurred throughout one's lifetime. Poor diet, lack of exercise, and exposure to ultra violet light all cause oxidative damage. For example, ultra violet light is known to generate reactive oxygen species (ROS), such as superoxide, singlet oxygen, hydroxyl radicals, and hydrogen peroxide, in the skin. These ROS are known to degrade collagen in the skin and to decrease the ability of fibroblasts to produce collagen.
Collagen is the primary protein of connective tissue, which includes cartilage, bone, tendon, teeth, and skin. Collagen (in a pre-processed form called pro-collagen) is assembled in cells and consists of three polypeptides wound around each other in a triple helix form, which is stabilized by intrachain disulfide bonds. After the helical molecule is assembled and modified in the cell it is secreted into the extracellular medium and further processed to a mature form (tropocollagen).
Matured collagen molecules assemble into fibrils in the extracellular space in a staggered, parallel, fashion wherein the molecules are stabilized in this fibril pattern by covalent cross-linking bonds between the N-terminus of one molecule and the C-terminus of another. The collagen fibrils are interlaced and branched in skin.
Indeed, these interlaced, branched collagen fibrils provide the skin with its shape and firmness, while another skin protein, elastin, provides skin with its elasticity. Elastin coils and recoils like a spring and accounts for the elasticity of structures such the skin, blood vessels, heart, lungs, intestines, tendons, and ligaments. Elastin is normally not produced by the human body after puberty and aging begin.
Like all other proteins in the human body, collagen and elastin are constantly being degraded. Enzymes that degrade collagen and elastin are known as matrix metalloproteases (MMPs). These enzymes can be stimulated by ROS. Some known MMPs include collagenase, elastase, MMP-1, and MMP-9. Collagenase is an enzyme produced by fibroblast like synoviocytes that degrades collagen. Elastase degrades elastin. MMP-1 cleaves fibrillar collagens, such as types I, II, and III, resulting in denatured collagens (gelatins) that are further degraded by MMP-9, which degrades laminin and type IV collagen, components of the basement membrane. Thus, these MMP enzymes are involved in the reduction of collagen and elastin in the skin, which leads to the appearance of fine lines, wrinkles, age spots, and sagging skin.
Like loss of collagen and elastin due to oxidative damage from ROS and MMPs, loss of moisture contributes to skin aging. Indeed, the skin's capacity to retain water decreases with age, making the skin more vulnerable to dehydration and wrinkling. Lipids and fats in the skin help combat water loss by providing an epidermal barrier. This barrier also hinders the growth of bacteria, which can cause skin irritation and sensitivity, both of which contribute to aging of skin.
Therefore, a formulation containing oxidizable or antioxidant nutrients to combat ROS, oxidative damage, and loss of collagen and elastin, as well as agents that hydrate the skin or increase the synthesis of lipids in the skin, would be useful for improving the appearance, texture, and moisture of the skin and maintaining general skin health.